Separating the role of stratospheric final warming in the Southern Hemisphere climate trends

The stratosphere experiences a seasonal transition from westerlies in the winter to easterlies in the summer, with a final warming event in the spring. Observations and models have shown that the date of stratospheric final warming in the Southern Hemisphere has been delayed over the past few decades (~10 days per decade) owing to stratospheric ozone depletion. We will present a new way to characterize the downward influence of ozone depletion by considering the change in the final warming date. The zonal wind trend is separated by the trend due to a delay in the final warming date and the trend due to the rate of seasonal transition about the final warming. The latter describes the difference between a faster zonal wind deceleration in an early final warming year and a slower deceleration in a late final warming year. Interestingly, it is found that the stratospheric zonal wind trend is associated with a delay in the final warming date, and that much of the downward influence in the troposphere is accompanied by the change in the rate of stratospheric seasonal transition. The decadal trend will be compared with interannual variability as well as the internal variability of the atmosphere.